Why is it that some people just can't resist a piece of cheesecake, while others quickly lose interest? The answer - scientists now suspect - may be on the tip of their tongues.

A newly formed alliance of health, genetic and medical researchers are beginning to divide the world into ``taste groups'' - supertasters, who are acutely sensitive; the middle range, and the so-called nontasters, who can barely sense the bite of pepper or the bitter tang of grapefruit.

It appears that genes regulate such sensitivities - controlling the number of taste buds on the tongue. And, it also appears, that the so-called supertasters register the creamy feel of fat so quickly that a little may go a long way. By contrast, the nontasters may need to move onto a second piece to get the same sense of satisfaction.

``Our working hypothesis is that perception of being satisfied is extremely important,'' said Valerie Duffy, a professor of nutrition at the University of Connecticut. ``And that supertasters feel this much faster.''

Not surprisingly, Duffy and her colleagues, gathered Sunday at the national meeting of the American Association for the Advancement of Science, have found that supertasters tend to be thinner and to maintain low-fat diets more easily.

In one study looking at elderly women, Yale University researcher Laurie Lucchina found that the taste-sensitive group were basically indifferent to high-fat dairy foods. She reported that they also had ``lower body mass'' overall than other women in the study and healthier cholesterol counts. Another study found that because supertasters tongues are so sensitive, they are easily irritated by alcohol. Chronic drinkers, it turns out, tend to be nontasters.

Linda Bartoshuk, a professor of medicine at Yale, said the specific gene that controls taste receptors has not been identified. But researchers say it appears to control not only the number of taste buds on the tongue but the structures that hold them, called fungiform papillae.

Those structures are connected to powerful nerves that are sensitive to both taste and touch. That explains why fat produces a touch sensation - creaminess - in the mouth. And why some extremely spicy compounds, such as the capsaicins found in chili peppers, can also produce a touch sensation, the physical feel of a burn.

Supertasters, obviously, have a lot more papillae and taste buds on their tongues. The range can be extreme. Nontasters have been with as few as 11 papillae per square centimeter. The highest known supertaster have 1,100 in the same space.

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